1. Field of the Invention
The present invention relates generally to an optical modulator for modulating light and more particularly, to an optical modulator using an electro-optic crystal.
2. Description of the Prior Art
An optical modulator using an electro-optic crystal can perform a high-speed operation. Thus, conventionally, the electro-optic crystal has been used for modulating a light signal which is transmitted through an optical fiber. In FIG. 1 showing one example of an optical modulator, electrodes 2 and 3 are provided on upper and lower surfaces of the electro-optic crystal 1. A modulating signal generating apparatus 4 is connected to the electrodes 2 and 3. A predetermined voltage is applied between both the electrodes 2 and 3 by the modulating signal generating apparatus 4. In addition, a polarizer 5 on an input side and an analyzer 6 on an output side are provided spaced apart from the electro-optic crystal 1 by a predetermined interval along a light entering direction (represented by an arrow A). Arrows illustrated in the polarizer 5 and the analyzer 6 indicate a direction of a plane of polarization.
In general, an electro-optic crystal is a ferroelectric substance, which has both piezoelectric and pyroelectric characteristics. Conventionally, an electro-optic crystal has been applied to a temperature sensor and an electric field sensor utilizing the foregoing characteristics.
However, piezoelectric and pyroelectric capabilities of the electro-optic crystal are significantly lowered, as compared with, those of a separate piezoelectric and pyroelectric bodies. Thus, it is very difficult to generate pyroelectric charges by heating the electro-optic crystal itself and to modulate light using a voltage based on the pyroelectric charges. In addition, from the relation between the direction of polarization in the electro-optic crystal and anisotropy in a dielectric constant of the crystal, the design of an efficient element is difficult.
Thus, a low-cost temperature sensor and electric field sensor having high sensitivity using the electro-optic crystal cannot be substantially achieved.